The long-term goal of these studies is to understand the regulated assembly, structure, and functional roles of cartilage extracellular matrix components during development. To reach this goal, we will use a combination of DNA cloning, immunohistochemistry, and transgenic mice technology to analyze the expression and function of the short-chain collagen X in hypertrophic cartilage, and of the FACIT components IX and XII in cartilage development. The cloned mouse genes for these collagens will be used to make vectors for gene targeting by homologous recombination in embryonic stem cells, as well as constructs designed to produce dominant negative suppressor mutations in mice. Analysis of mice with such engineered defects will provide novel and important information about the role of collagen components in cartilage structure and development as well as provide animal, models for cartilage abnormalities in man. Finally, we will use a sensitive subtractive hybridization technique to clone cDNAs encoding factors involved in the transition from small chondrocytes to hypertrophic chondrocytes in maturing cartilage. This will provide the initial entry point for a detailed molecular understanding of how the transition between the two chondrocyte states is regulated, and thus a basis for examining the molecular defects in many chondrodysplasias.